This invention pertains generally to guidance systems for missiles and particularly to systems of such type wherein optical sensors are used to detect targets.
It is well known in the art that optical sensors may be incorporated in guidance systems for many different types of missiles. Such sensors ordinarily include focusing means, reticle means and detector means which are so related to one another that radiant energy from a target ultimately may cause electrical signals indicative of the line of sight between the target and the missile to be generated. Such electrical signals then may be processed along with positional signals to derive the requisite guidance commands to effect an intercept.
In some types of optical sensors the focusing means, the reticle means and the detector means are mounted on a gyroscopically stabilized platform within a two-axis gimbal set. Unfortunately, however, it is extremely difficult and expensive to make satisfactory optical sensors, especially when the detector means requires cryogenic cooling.
In order to reduce the complexity of an optical sensor a so-called "free gryo" configuration is sometimes used. In such a configuration the detector means is fixed to the body of the missile with the focusing means and at least a part of the reticle means mounted in a fixed relationship to one another on a universal joint. The focusing means and the part of the reticle means so mounted may be rotated and turned together through a range of gimbal angles. It will be appreciated that, if a detecting element is located at the center of the universal joint and if the received optical energy need not be focused precisely on such an element, the "free-gyro" configuration may be made much more easily with a fewer number of components. Further, it will be recognized that the "free-gyro" configuration may operate satisfactorily through an appreciable range of gimbal angles.
A different situation obtains when (as in cases wherein arrays of detecting elements are required) a detecting element cannot be mounted at the center of the universal joint or precise focusing is required. In such cases the range of gimbal angles through which satisfactory operation is possible is severly restricted.